In general, the principle of designing a lens is to let a traveling light produce an optical path difference (thickness*refractive-index). Since the conventional spherical lens has a thickness increases with the optical power, therefore an improved method uses a Fresnel lens to divide the thickness into a smaller periodical structure was proposed. But the manufacture of the mold for the Fresnel lens is very complicated and relatively difficult, and the optical performance has the issues of a high chromatic dispersion and low diffraction efficiency. Therefore, conventional flat lenses such as glasses lenses achieve a change of the optical path difference by changing the refractive index distribution.
Wherein, the liquid crystalline polymer has the unique birefringence feature, and thus it can be used for the design of a flat lens. Since the liquid crystalline polymer also has the properties of dielectric anisotropy, therefore the electric field distribution can be applied to manufacture an electrically tunable liquid crystal lens. However, the present liquid crystalline polymer film only has the same refractive index distribution. In other words, each position of the liquid crystalline polymer film has the same focal length. Therefore, the present liquid crystalline polymer film with the design of a single focal length cannot be used freely with other lens. Due to the liquid crystalline polymer film having the design of a single focal length, additional components are required to change the refractive index distribution of the liquid crystal lens for manufacturing the electrically controlled liquid crystal lens.